Magnetoresistance in Co/ZnO Films

[Co(0.6 nm)/ZnO( x nm)] ₆₀ (x=0.3 - 3) films were deposited on glass substrates by magnetron sputtering, and then annealed in vacuum. The large negative magnetoresistance of -10.4% is observed in the as-deposited [Co(0.6 nm)/ZnO(0.4 nm)] ₆₀ film. When ZnO layer thickness is increased from 0.3 to 3 nm, MR ratios of the as-deposited Co/ZnO films are gradually decreased and MR ratios of the annealed films are increased, which might be attributed to the transformation of the structures from the multilayers to granular films during annealing. And the postannealing process makes the magnetism of the films transform from superparamagnetism to ferromagnetism due to Co precipitation in granular films after annealing.